1. Field of the Invention
The invention concerns a system for selective treatment of a traveling paper web by coating or impregnating in in-line arrangements.
2. Description of the Related Art
Voith Product Brochure No. "p 2771" discloses a so-called "Speedsizer" wherein the coating mixture is applied on both sides of the web simultaneously (FIGS. 2 through 8) In all of these illustrated embodiments, the web sections (paper trains) still are relatively long. This is evident especially in FIG. 8, which shows the retroactive installation of a coater for double-sided application of the coating mixture in an existing paper machine. The coater is followed by noncontact dryers arranged on both sides of the web, which necessitates an overall arrangement extending all the way into the basement. In addition to long paper trains, this variant entails disadvantages also in view of the necessary construction measures and tending options.
DE 43 13 628, which corresponds to co-pending U.S. patent application Ser. No. 08/229,173, now U.S. Pat. No. 5,469,636 involves long web sections and coaters and noncontact dryers that extend upwardly. The same disadvantages are present as in the aforementioned Voith Product Brochure.
Therefore, the problem underlying the invention is to provide a system where the surface treatment with a coating liquid, or impregnating, of a traveling paper web, can be performed with little expense, where the coaters required for existing dryer sections of a paper machine while nonetheless requiring only limited overall space, limited overall length, providing good tending options from the paper machine floor, and involving maximally short paper trains for the drying process. Additionally, the short unsupported paper trains are meant to enable a high runability, notably with high speeds and low web strengths.
This problem is solved by providing first and second dryer groups as well as first and second coaters to coat opposite sides of the web wherein the first coater is positioned after the first dryer group and the second coater is positioned before the second dryer group. Web deflectors follow the coaters.
According to the invention it is easily possible to retrofit an existing conventional dryer section with coaters and noncontact dryers for surface treatment of the traveling paper or cardboard web. It is possible as well to make use of the invention in the construction of a new paper machine.
The dryer section may be one as described, e.g., in DE 4 328 554 and consist of single-row dryer groups each with a single endless felt. Following the last single-felt dryer group is at least one dual-felt dryer group with several lower cylinders and several upper cylinders and with one upper felt and one lower felt. The dryer groups may be configured, if desired, in three rows or set obliquely, in so-called V-form.
The first coater to be installed is arranged preferably behind a double-row group of drying cylinders. The advantage of this is that the web can enter the first coater, if desired, with a final moisture content of, e.g., only 2%.
When a surface treatment or impregnation of the web is not desired, the solution according to the invention also enables at times the nonuse of the coaters integrated in the dryer section, where the path of the web may remain nearly unaltered. In such case, the afterdryer section may be utilized to increase the operating speed. This is possible because (without coating) less moisture must be removed from the web.
Overall, only a few drying cylinders, for example three, need to be removed, if coaters are installed into an existing dryer section.
The path of the paper web need not depart at any point from the normal space of the dryer section, so that the coaters can always be tended approximately from the paper machine floor.
The advantages resulting from a limited overall length, limited overall space requirements and very short unsupported paper trains are achieved by the arrangement of the coaters according to the invention, which at separate points treat once the underside and once the top side of the web, and by the arrangement of the following web deflection means, for example deflection rolls or noncontact deflection devices, which operate with unheated or heated air and are known as "air turn" or "air can" deflectors. Noncontact dryers are favorably coordinated with a drying cylinder fashioned as a deflection roll, i.e., the cylinder is preferably unheated. In the prior art, the noncontact dryers were arranged on both sides along the web path and, therefore, caused long paper trains.
Short unsupported paper trains also allow increased speeds of web travel, without inviting web breaks. In addition, the short unsupported paper trains allow with dry substance contents of the web .ltoreq.80% idle passage of the application area, when the applicators are not being used.
The invention will be explained hereafter with the aid of pictorially illustrated embodiments.